State-of-the-art MEMS vibratory gyroscopes typically use hemispherical geometries in conjunction with metal electrodes placed directly in contact with the mechanical resonator structure. As the metal electrodes are implemented, the high mechanical quality factor (Q) of the resonator is spoiled. Also the fabrication tolerance of the metal contacts can reduce the symmetry of the resonator. Reductions in Q and symmetry both reduce the gyroscope sensitivity and increase bias drift. Further, when conducting/semiconducting materials are used, such as Si, Ni, etc., the gyroscope either suffers from mechanical loss of the material or inherent asymmetry due to asymmetry of crystalline materials.
Many state-of-the-art approaches for shell resonators involve complex hemispherical geometries. P. Shao, L. D. Sorenson, X. Gao, and F. Ayazi, “Wineglass on-a-chip” Solid-State Sensors, Actuators, and Microsystems Workshop Hilton Head Island, S.C., Jun. 3-7, 2012, p. 275-278 of Georgia Institute of Technology describe an approach relying on final assembly with epoxy under a microscope. The ‘wineglass’ shaped SiO2 shells are conformally coated with TiN electrodes which reduce the intrinsic Q of the shell structure. The reported measured Q is less than 5.6E3, which is lower than desired. Also this approach is not a wafer scale approach and will likely have alignment and stability issues relating to the use of epoxy.
M. L. Chan, J. Xie, P. Fondal, H. Najar, K. Yamazaki, L. Lin and D. A. Horsley, “Micromachined Polycrystalline Diamond Hemispherical Shell Resonators” Solid-State Sensors, Actuators, and Microsystems Workshop Hilton Head Island, S.C., Jun. 3-7, 2012, p. 355-358 of University of California at Davis collaborating with University of California at Berkeley also describe a hemispherical shell resonator but fabricated from polycrystalline diamond. The reported measured Q is less than 3E3, which is lower than Ayazi's above, and lower than desired. The measured frequency splits are about 870 Hz on 34.68 kHz (˜2.5%), which leads to decreases in sensitivity and bias stability. Also, the resonant frequency of these structures appears to be very sensitive to anchor mounting radius, as a factor of ten times increase in frequency is measured (20 kHz to 200 kHz) for anchor depths varying from 5 μm to 30 μm. This variability is not desirable. Increasing anchor depth in this case corresponds to increasing anchor radius.
D. Senkal, C. R. Raum, A. A. Trusov, and A. M. Shkel, “Titania silicate/fused Quartz Glassblowing for 3-D Fabrication of Low Internal Wineglass Micro-structures” Solid-State Sensors, Actuators, and Microsystems Workshop Hilton Head Island, S.C., Jun. 3-7, 2012, p. 267-270 of University of California at Irvine describe a hemispherical inverted wineglass structure which relies on individual laser ablation to release structures, which is again not a wafer scale approach. An additional problem resulting from this release technique is that the laser ablation for rim release of the inverted wineglass structure will likely perturb symmetry of rim and therefore increase frequency splits and degrade the gyroscope bias stability.
What is needed is a shell gyroscope structure with improved sensitivity and frequency stability. The embodiments of the present disclosure answer these and other needs.